Unseptnilium
Unseptnilium, Ust, is the temporary name of element170. NUCLEAR PROPERTIES At least one set of theoretical values for half-lives and decay modes of Usn have been constructed for neutron count up to N = 333(3). It predicts isotopes ranging from Usn 439 to Usn 502 in three bands: Usn 439 and Usn 440, Usn 461 to Usn 482, and Usn 499 to Usn 502. Examination of pp 15 & 18 of Ref. 3 indicates that Usn 461 through Usn 482 are part of the expected pattern of alpha-decaying nuclei centered on the N = 308 shell closure. Isotopes between Usn 468 and Usn 479 are predicted to have sub-millisecond half-lives and to decay by alpha emission. The other isotopes in this band have sub-microsecond half-lives and most decay by alpha emission, which is consistent with neutron shell closure at Usn 478. Usn 439 and Usn 440 are very neutron-poor, and not located in the vicinity of any suggested shell closure; they appear to be artifacts of the sort common near the edges of models. Usn 499 to Usn 502 might indicate a shell closure near N = 330, but they are also located in a region whose patterns of half-lives and decay modes indicates that the model may have reached the limits of its capability. What Ref. 3 can’t do is describe heavy isotopes of Usn. It is possible to use a first-order, liquid-drop approach to guess at what lies there. At least two computations of the neutron dripline’s location up to Z = 175 exist(4),(5), and since they give similar results, the maximum possible size of a Usn nucleus can be set slightly above the values computed, allowing only a small margin for error. This gives Usn 608 as the heaviest possible Usn isotope. Similarly, a realistic lower bound can be set by requiring that the amount of energy needed to stabilize a nucleus be no more than twice what is needed to stabilize Usp 471. Within this range, the liquid-drop model can be used to indicate the amount of structural correction energy needed to allow a drop of nuclear matter to survive for the 10^-14 sec needed for electromagnetic interactions (such as binding an electron) to become important. Structural correction required for Usn 608 itself is around 1 MeV, which means all Usn drops will fission quickly without structural stabilization. In general, it is not possible to describe structural correction energy. What can be predicted are neutron and proton shell closures, for which correction energy is expected to be particularly large. Neutron shell closures have been predicted at N = 406(5),(6), 370(5), 318(7), and 308(3). The isotope Usn 576 requires 1.5 MeV of structural correction, which means isotopes in the Usn 566 to Usn 581 band are likely. (See “Formation” for additional significance of these nuclei.) Usn 540 requires 1.5 MeV of structural correction, which means isotopes in the band Usn 530 to Usn 545 are also likely. All isotopes in both bands should beta-decay with half-lives under a second. On the other hand, Usn 488 requires 4 MeV of correction energy, which means it is likely to stabilize some nuclei in its vicinity. Ref. 3 does not show a pattern of nuclides which indicate a shell closure at N = 318. Usn 478 requires 5.5 MeV of correction energy, which is realistic for a strong neutron shell closure, such as the one predicted at N = 308, so the liquid-drop picture isn’t unrealistic. Extrapolated atomic properties Several predictions for the ground state electron structure of Usn agree that it will have p-block character, with two 9s, two 9p1/2, and two 8p3/2 electrons available for bonding. Electrons in Usn can probably be described in terms of time-independent orbitals, but there is a some chance that the conventional time-independent orbital concept does not apply to atoms with this high a value of Z. Calculation of electron properties require that nuclear charge be distributed over the nucleus' actual volume. In addition, there is some chance that differing nuclear shapes may produce different electron configurations in different isotopes. (Different isotopes would be different elements in the chemical sense.) Except in the laboratory, Usn is expected to exist only in environments too hot for ordinary chemistry to occur. Formation Ions of this element may form when material from roughly 1 km depth is ejected from a disintegrating neutron star during a merger. There is a possibility that beta decay from dripline nuclides stabilized by the N = 406 closure, enhanced by the Z = 164 proton shell closure, will allow some isotopes in the vicinity of Usn 565 to Usn 577 to form in quantity during such a merger. It improbable that nuclides between Usn 530 and Usn 545, or lighter, can form in this way. Fusion or multinucleon transfer reactions in the polar jets emanating from a neutron star or black hole might produce lighter isotopes, including those in the Usn 461 to Usn 482 band. Quantities produced by this method are very small. REFERENCES 3. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011. 4. "Neutron and Proton Drip Lines Using the Modified Bethe-Weizsacker Mass Formula; D.N. Basu et al; Int.J.Mod.Phys.; arXiv:nucl-th/0306061; url: https://arxiv.org/abs/nucl-th/0306061 5. “Single Particle Levels of Spherical Nuclei in the Superheavy and Extremely Superheavy Mass Region”; H. Koura and S. Chiba; Journal of the Physical Society of Japan; DOI 10.7566/JPSJ.82.014201; Jan. 2013. 6. "Magic Numbers of Ultraheavy Nuclei"; V. Yu Denisov; Physics of Atomic Nuclei, v. 68, no. 7, pp 1133-1137; 2005. 7. “The Highest Limiting Z in the Extended Periodic Table”; Y.K. Gambhir, A. Bhagwat, and M. Gupta; Journal of Physics G: Nuclear and Particle Physics. 42 (12): 125105. DOI:10.1088/0954 3899/42/12/ 125105. (12-12-19) References Category:Undiscovered elements Category:Alkaline earth metals Category:Radioactive